1. Field of the Invention
The present invention relates to perovskite materials and especially to colossal magnetoresistive materials used as an active dielectric medium in a capacitance apparatus and a method of using electrical pulses to change the non-volatile capacitance values, where each capacitance value is maintained without constant consumption of electric power.
More particularly, the present invention relates to a capacitance apparatus including a substrate having formed thereon a multi-layered, non-volatile, programmable or variable capacitive element or capacitor including a bottom conducting layer, an active layer, and a top conducting layer, where each capacitance value is maintained without constant consumption of electric power. The present invention also relates to methods for making and using the apparatus.
2. Description of the Related Art
Capacitors are one of the three basic electronic elements along with resistors and inductors that make up all passive electrical circuits. In many electric circuit applications, there is a need to change the capacitance value of a capacitor. Such application include non-volatile memories, filters, oscillators, modulators, resonance circuits, etc., in the computer and telecommunication industries, power generation and delivery in the utility industry, and in other fields such as electroacoustics, remote sensing and the like.
Early methods of varying the capacitance value of a capacitor used mechanical means. For example, a set of flat-plated electrodes are mounted on a rotating shaft. By rotating the shaft, the set of moving electrodes engages more or less with a set of fixed flat-plated electrodes hence change their common area. The capacitance of the whole assembly therefore changes accordingly. An alternative method involves adjusting a screw, which adjusts the gap between two opposite electrodes to reach capacitance variation. With these devices automation of capacitance change is difficult if not impossible.
Recent capacitance-varying semiconductor devices are collectively known as varactors. A varactor is a p-n junction diode or a Schottky junction diode that is properly doped with impurity elements. A space-charge region depleted of charge carriers, known as the depletion region, exists at the junction. The depletion region has a build-in capacitance, which is inversely proportional to the width of the depletion region. By applying different values of reverse biases to the junction, the width of the depletion region changes and the capacitance of the junction, therefore, changes accordingly. See, e.g., Robert L. Boylstad and Louis Nashelsky, xe2x80x9cElectronic Devices and Circuit Theoryxe2x80x9d, pp814-818, 7th edition, Prentice Hall, 1999, Sata, et al, U.S. Pat. No. 4,449,141, May 15, 1984; Sakai, et al, U.S. Pat. No. 4,529,995, Jul. 16, 1985, incorporated herein by reference.
Since a varactor is a voltage controlled device, automation of capacitance change is easy. The other advantage of varactor over the early capacitance-varying devices relates to the maturity of semiconductor device integration.
The major drawback of a varactor is its constant consumption of electric power during the maintenance of a particular capacitance value, since a constant bias voltage must be applied to the varactor during this period. The power consumption is manifested as dissipation due to reverse-bias leakage current. Collectively, on an integrated circuit, this power consumption can be significant and depends upon the extent of integration. The dissipated heat in turn heats up the circuit and may cause instability of the entire integrated circuit. Also, in critical applications such as in remote sensing, every effort is needed to save electric energy; this waste of electric power is therefore undesirable.
The second drawback of a varactor is the mutual influence between the bias voltage and the voltage of the active signal. Superimposition of these two voltages causes capacitance deviation from the originally desired capacitance value. This leads to performance deterioration, for example, frequency instability in an oscillator circuit or a resonance circuit.
The third drawback of the varactor is its volatile nature of capacitance change. As soon as the bias voltage is withdrawn from the varactor, the device completely losses its memory of its previously attained capacitance value.
Ferroelectric capacitance is a non-volatile capacitance. A ferroelectric capacitance can be partially changed by applying an electrical pulse with pulse duration shorter than the time period required to reach the spontaneous polarization of the ferroelectric film. Partial polarization changes (capacitance changes) in ferroelectric films induced by short electrical pulses have been proposed as a pulse frequency modulation (PFM) system to be used in neuron circuits (see, e.g., xe2x80x9cProposal of adaptive-learning neuron circuits with ferroelectric analog-memory weights,xe2x80x9d Hiroshi Ishiwara, Japan Journal Applied Physics, Vol. 32, PP. 442-446, 1993). However, non-volatile ferroelectric capacitors and PFMs are limited in applications due to the retention problems of ferroelectric materials and destructive read-out processes.
Thus, there is a need in the art for a variable capacitive apparatus with a basic structure that can overcome the above articulated drawbacks of its predecessors, and a convenient and retentive method to actuate the capacitance changes.
The present invention provides a non-volatile, simple-structured, robust, reliable, programmable or variable capacitor, where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention also provides a variable, non-volatile capacitor including a multi-layered thin film structure having a first or bottom conducting layer and a second or top conducting layer with an active dielectric layer interposed therebetween, where the structure changes capacitance in response to an electric pulse applied thereto and where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention also provides a non-volatile, variable capacitance apparatus or capacitor including a substrate having a multi-layered thin film structure deposited thereon, where the structure includes a first or bottom conducting layer and a second or top conducting layer with an active dielectric layer interposed therebetween, where the structure changes capacitance in response to an electric pulse applied thereto and where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention also provides a circuit including at least one non-volatile, variable capacitor apparatus of this invention, where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention also provides a circuit including a least one simple-structured, non-volatile, programmable capacitor capable of being set to two or more capacitance values, where the capacitance of the capacitor can changed to one of its allowed non-volatile values by applying at least one electric pulse to the capacitor depending on a desired circuit output, where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention also provides a simple two-terminal capacitive apparatus or capacitor including a perovskite material such as a colossal magnetoresistive (CMR) material, which comprises an active dielectric medium sandwiched or interposed between to conducting layers, where the active medium changes its capacitance when exposed to one or more electric pulses, where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention provides a new simpler method to set and/or tune a capacitance value of a non-volatile programmable or variable capacitor of this invention and to a method to reproducibly erase and sense the capacitance of the capacitors of this invention by applying one or more electric pulses to the capacitor, where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention also provides a method for adjusting an output of a circuit including the step of changing a capacitive value of at least one capacitor of this invention included in the circuit by applying one or more electric pulses until a desired circuit output is achieved, where each capacitance value of the capacitor is maintained without constant consumption of electric power.
The present invention also provides a method to tune a circuit including the steps of providing a circuit including at least one variable capacitor of this invention, where each capacitance value of the capacitor is maintained without constant consumption of electric power; obtaining a first circuit output; comparing the first circuit output to a desired circuit output; applying an electric pulse to at least one variable capacitor of this invention to change a capacitance of the capacitor from a first capacitance value to a second capacitance value, obtaining a second circuit output and comparing the second output to the desired output. The method can also include repeating the applying step, the second obtaining step and the second comparing step until a difference between the actual circuit output and the desired circuit output is a minimum. The application can also be run in reverse to detune a circuit.